Brake control means



Jan. 20, 1942.

J. CANE'ITA E 2,270,414

BRAKE CONTROL MEANS Filed Aug. 15, 1940 I 2 Sheets-Sheet 1 Tl ON null ll lll h duh INVENTO S JOHN.CAN5TTA PA-UL N. BOSSART Way,

ATTORNEY Jan. 20, 1942. J. CANETTA ETAL BRAKE CONTROL MEANS Filed Aug. 15. 1940 2 Sheets-Sheet 2 MIN QM. NW 9% mm A QW MN QN RN 7 RN RN 3% wm mm 9 mm mm WW mm m M @N N m Nil 1 IH \n WW 5 m hvv mNhNQNE mm R mm w M J Q N N T EN fi X M j m\ WW L m mm c R F g Q Q a m m9 @Q Q N mm 99 no b1 6 nor :wQ V? @Q Q: P & og my 1- R9 .03 .2

A'ITORNEY Patented Jan. 20, 1942 UNITED STATES PATENT OFFICE BRAKE CONTROL MEANS Application August 15, 1940, Serial No. 352,770

12 Claims.

This invention relates to brake control means for vehicles, such as railway cars and trains, and has particular relation to brake control apparatus of the type having means responsive to the rate of change of speed of individual wheels or wheel units adapted to control the degree of application of the brakes associated with such Wheel or wheel units in a manner to prevent the sliding thereof.

As is well known, if the degree of application of the brakes associated with a vehicle wheel becomes sufficient to exceed the limit of adhesion or rolling friction between the wheel and the rail or road surface on which it rolls, the wheel decelerates promptly at an abnormally rapid rate to a locked or non-rotative condition and slides. Sliding of railway car wheels is objectionable because it develops flat spots on the wheels, thereby necessitating replacement or repair of the wheels.

In the subsequent description of my invention, the term slide refers only to the dragging of a wheel along the rail or road surface in a locked condition. The rotation of a vehicle wheel at a speed less than a speed corresponding to vehicle speed at a given instant is referred to as slip or a slipping condition. The distinction between the terms slide and slip should accordingly be borne in mind.

Under the most favorable conditions of adhesion or rolling friction between a wheel and the rail on which it rolls, a certain maximum rate of rotative deceleration of the wheel due to braking is possible without causing the wheels to slip. The rotative deceleration of a wheel at a rate exceeding a certain high rate, which is never attained while the wheel is not slipping, is therefore positive indication of a slipping condition. It has heretofore been proposed to provide various types of devices, either mechanical or electrical in nature, responsive to the rate of rotative deceleration of a vehicle wheel for automatically and instantly effecting a rapid reduction in the degree of application of the brakes associated with a wheel when the wheel begins to rotatively decelerate at a slipping rate. This automatic and instantaneous rapid reduction in the degree of application of the brakes associated with a slipping wheel causes the wheel to cease decelerating and begin to accelerate back toward a speed corresponding to vehicle speed, without actually decelerating to a locked or nonrotative condition and sliding.

Up to the present tirrie, the proposed devices which are responsive to the rate of rotative deceleration of a vehicle wheel have been of the rotary inertia type or of the generator type. Moreover, such devices have been associated directly with the vehicle wheel or the axle connecting a pair of wheels, as by mounting the devices in a separable casing attached to the journal at one end of a wheel axle in place of the usual end'cover and in such manner that the rotary element of the devices are in coaxial coupled relation to one end of the wheel axle.

Due to the inherent weight of such devices and the fact that they are subject to the constant shock and vibration due to travel of the vehicle along the rail, the friction and wear on the bearings of the rotatable elements of the devices has been found to be excessively high. Such friction may, if permitted to continue long enough, interfere with the accuracy and sensitivity of the devices to the rate of change of speed of the vehicle wheel and will in any case necessitate undesirably frequent servicing or repair.

It is an object of our present invention, therefore, to provide a brake control equipment of the general type indicated above and characterized,-according to our invention, by a novel type of apparatus responsive to the rate of change of speed of a vehicle wheel which inherently avoids the difiiculties presented by prior devices.

In carrying out the above object, we have utilized apparatus similar in some respects to the apparatus disclosed in the co-pending application Serial No, 342,935, of John Canetta, one of the present joint applicants, filed June 28, 1940,

- and assigned to the same assignee as the present application. In this copending application a'commutator device is provided which is rota able according to the rotational speed of a wheel of a vehicle for alternately charging a condenser to the voltage of a substantially constant voltage source and discharging the condenser into a discharge circuit repeatedly in rapid succession so as to produce a pulsating direct-current in the discharge circuit substantially proportional to the rotational speed of the wheel. Our present invention so modifies the discharge circuit of the apparatus shown in the copending application as to cause pick-up of a relay therein only in response to deceleration of the vehicle wheels at a rate exceeding a certain rate occurring, for example, when the wheel slips.

It is another object of our invention to provide apparatus of the character indicated above and further characterized by an arrangement in the discharge circuit whenever a vehicle wheel rotatively decelerates at a rate exceding a certain substantially uniform rate notwithstanding variation in the speed of travel of the vehicle over a wide range.

It is another object of our invention t provide brake control equipment for a single car or a train of cars including electrical wheel-slipresponsive apparatus of the type indicated in the foregoing objects and further characterized by an arrangement for compensating for the number of cars in the train.

The above objects, and other objects of our invention which will be made apparent herein-. after, are attained by several embodiments of our invention subsequently to be described and shown in the accompanying drawings wherein,

Fig. 1 is a diagrammatic view illustrating the, principal object of our invention as applied to two separate wheel units of a car, as for example the two wheel units of afour-wheel truck;

Fig. 2 is an enlarged fragmental view. partly in section, showing details of construction. of the commutator devices associated with the indi.-- vidual wheel units shown in Fig. 1,

Fig. 3 is a. diagrammatic view, showing a de velopment of the commutator device in Fig. 2 and, illustrating the relative positions. of the brushes. associated with the commutator device,

ig. 4, is. a fragmental diagrammatic view.

showing amodification of the apparatus, in Fig. l and Fig. 5 is a diagrammatic View, showing an.- other modificationof the apparatus in Fig. 1,

and adapted for operation. in connection with a.

single railway car or a train of cars.

Description of equipment shown in Fig:- 1

Referring to Fig. 1, the equipment; sh'own is illustrated as applied to a four-wheel truckhav ing apair of wheel units H and], each unit'come prising two wheels, only one of which is shown, connected by and fixed at opposite ends to an axle I2 in well-known manner. Forconvenience and simplicity, details of the truckstructure are omitted. Similarly, the brake shoes associated with the wheels and they brake operating lever mechanism or brake rigging therefor have been omitted, it being understood that, the brakes may be of the conventional clasp. shoetype applied by supplying fluid under pressure to brake cylinders I 3 and released by. releasing fluid under pressure therefrom.

The supply of fluid under pressure to the. brake cylinders I3 and the release of fluid under. pres.- sure therefrom may be effected under the con-.. trol of the operator of the vehicle by any suit.- able and well-known type of fluid pressure brakecontrol apparatus. For. simplicity, the operatob controlledapparatus is illustrated as comprising a train pipe I5, hereinafter called the control pipe, which may extend from car to car throughout a train, the sections on successive 7 cars being connected by suitable h'ose couplers (not shown) in conventional manner; a reservoir l6 hereinafter referred to as the main reservoir, which is maintained charged at a suitable fluid-pressure, such as one hundred pounds. per square inch, from a suitable fluid compressor not shown; and a manually operatedbrake valve I! of well-known self-lapping type for con-- trolling the fluid pressure in the control pipe I5.

The pressure chamber at one side of the usualpiston in each brake cylinder I3 is connected. to the control pipe I5 by acorrespondingbranch.

pipe I8 so that the fluid pressure in the brake cylinder I3 normally corresponds to the fluid pressure established in the control pipe I5.

The brake valve I! has an operating handle IIa which is effective in its normal brake re lease position through the medium of a rotary operating shaft to condition the self-lapping mechanism of the brake valve I! to exhaust fluid under pressure from the control pipe I5 through an exhaust port and pipe I9 to establish atmospheric pressure in the control pipe and correspondingly in the brake cylinders I3. When the brake valve handle I'I'a. is shifted in a horizontal; plane out. of its normal release position into a, sor-calledi application zone, the self-lapping mechanism of thebrake valve is operated to cause fluidunder pressure to be supplied from the main reservoir I5 to the control pipe I5, the fluid pressure established in the control pipe corresponding substantially to the degree of displacement of the brake valve h'andle I'Ia. out of itsbrake, release position. Thus, by shifting the brake valve, handle IIa todifferent positions in the application zone having different degrees of displacement with respect. to. the release po.- sition thereof, the pressure in the control pipe I5 and, the brake cylinders I3 may be correspondingly controlled by the operator.

If the pressure in the control pipe I5; isreduced due to leakage or other causes referred to hereinafter. the self-lapping mechanism ofthe brake valve automatically operates to supply fluid under pressure to the control pipe. to maintain a. pressure thereincorresponding to the positionof' the brake valve handle. This pressure maintainin feature should be borne in. mind in connection with the subsequent description of the operation of the equipment.

According to our invention, there is. interposed in the branch pipe I8 leading. to. the brake cylinder I3. for each wheel unit a. double-beat magnet. valve of suitable type which iscontrolled by a. corresponding electrical apparatus. 22. responsive. to therotative deceleration of the corresponding wheel unit. at a. slipping rate so as to. release fluid, under pressure fromv the. asso-.

ciated brake cylinder I3. independently of. the operator-controlled apparatus.

The electrical apparatus 22- comprises a, com.- mutator device 23 secured to the end of the. wheel axle, 12 of eachwheel unit inthe manner shown in Fig. 2; an electrical. condenser 24;. a. source.

of direct-current voltage, such as a storage, battery, 25; three contact fingersor brushes. 26., 2.1. and 28,- a condenser unit 29.; a relay 3i. ofthe polarizedltype; and a non-inductive resistor 32.

As willbe apparent in Fig. 2, thecommutator.

device 23 may comprise a base member 36, in.-

the form of a solid cylinder. of. insulating. material with a flange 37 at one end secured as by a plurality of screws 38 to the. end. of. the. axle. I2 of a wheelunit in coaxial relation to the. axle.

and rotatable therewith. The commutator device further comprises a ring 39 ofsuitable metal, such as copper, brass or alloysv thereof. whichv is embedded in thjeouter. end surfaceof theinsulating base or otherwise suitably. affixed thereto.

portion having a plurality, illustratively shown The ring 39 comprises. a continuous The brushes 26, 21 and 28. may be-carriedflbya suitable brush holder in conventional manner, not shown, which is in turn supported from or secured to the inside of the axle journal. As indicated in Figs. 2 and 3, the brushes 2'! and 28 are located in the same transverse plane in alignment with each other so as to engage the fingers 41 of the ring 39 whereas the brush 26 engages the continuous portion of the ring 39. For illustrative purposes, the brushes 21 and 28 are separated by an angle of approximately 157 although, as will hereinafter appear, any other uitable angular relation thereof for effecting the same result may be employed. The brush 26 is indicated as having a certain angular relation to the brushes 21 and 28 but, as will be apparent from subsequent description the angular position of this brush relative to brushe 2! and 28 is immaterial.

As indicated in Fig. 3, the angular spacing between the two brushes 21 and 28 is such that these brushes are alternately engaged by the contact fingers 4| of the ring 39 of the commutator device, as the base 36 is rotated on its axis. Thus, when the brush 28 engages a contact finger 4|, as shown, the brush 2! is not engaged by a contact finger, and vice versa.

It will thus be understood that the commutator device 23 is efiective, upon rotation, to alternately connect the brush 26 to th brushes 2'! and 28.

As will be seen in Fig. 1, the brush 2'! is connected by a wire 45 to one terminal of the battery 25, hereinafter taken to be the positive terminal, and that the brush 26 is connected to the opposite or negative terminal of the battery 25 by a wire 46 in which is interposed the condenser 24. The negative terminal of the battery 25 is grounded as at 41. Thus, when the commutator device 23 connects the brushes 26 and 21, a circuit is established for charging the condenser 24 to the voltage of the battery 25.

Connected between the brush 28 and ground at a point 48, is a circuit including two parallel branches, one of which includes the resistor 32 and the other of which includes the condenser unit 29 and the polarized relay 3| in series relation. Accordingly, when the commutator device 23 connects the brushes 26 and 26, the electrical charge stored in the condenser 24 is discharged through the resistor in the discharge circuit.

As in the copending sole application, Serial No. 342,935 of John Canetta mentioned above, the con-denser 24 and its charging circuit are so designed as to have a charging-time constant that is small relative to the time of charging or the time that the charging circuit is closed. Accordingly, each time the charging circuit is established, the same quantity of electricity is stored in the condenser independently of the time of connection thereof to the battery 25, assuming the battery 25 to have a substantially constant voltage at all times. Suitable charging and voltage-regulating apparatus (not shown) may be provided for maintaining the voltage supplied by battery 25 at a constant value.

It will be apparent that the quantity of electricity so stored in condenser 24 will be a constant because the quantity Q of electricity, in coulombs, stored in a condenser is equal to the product of the capacitance C, which is a constant, of the condenser in farads and th voltage E impressed across the condenser. This may be expressed in the form of the following equation:

(1) Q=CE If the nature of the discharge circuit were such that upon the establishment of the discharge circuit, the quantity Q of electricity stored in the condenser 24 were completely discharged then the alternate charging and discharging of the condenser repeatedly in rapid succession would produce a pulsating direct-current in the discharge circuit which would be directly proportional to the frequency or number of times per second that the discharge circuit is established.

As is well known, the unit of electrical current, the ampere, is the equivalent of a coulomb of electricity per second. Thus, th current in the discharge circuitin amperes would be theoretically equal to the quantity Q, in coulombs, discharged from the condenser 24 each time the discharge circuit is established multiplied by the frequency) or the number of time the discharge circuit is established per second. This relation may be expressed mathematically by the equation:

It will be readily apparent from Equation (2) that assuming Q to be a constant, the current I in the discharge circuit varies in direct proportion to the frequency f.

Obviously, the frequency of establishment of the discharge circuit depends not only upon the number of revolutions per second of the commutator device 23 but also on the number of contact fingers 4|, which make and break the discharge circuit a corresponding number of times during each revolution. Thus the frequency may have any desired range by selecting a desired number of contact fingers 4| for the commutator device In actuality, the same quantity of electricity is not discharged from condenser 24 each time the discharge circuit therefor is established because of the variation in the voltage-drop across the resistor 32 with variation in the rotational speed of the commutator device 23. This will be apparent when, by analogy to Equation 1, it is understood that the quantity of electricity discharged from a condenser is equal to the capacitance of the condenser multiplied by the change in the voltage impressed on the condenser. Assuming that Q is the quantity of electricity in coulombs discharged from a condenser, C is the capacitance of the condenser in farads, E is the initial voltage impressed on the condenser, and E1 is the reduced voltage impressed on the condenser, the quantity of electricity discharged may be expressed mathematically by the equation:

Obviously, if the voltageon a condenser is reduced to zero, the quantity of electricity discharged from the condenser is equal to the entire quantity of electricity stored on the condenser. Similarly, if the voltage impressed on the condenser is reduced from a higher to some lower value, the quantity of electricity discharged from the condenser will be some fraction of the quantity stored on the condenser.

It will be further apparent that the polarity of the voltage-drop across the resistor 32 in the discharge circuit of the condenser 24 is such that the change in voltage on the condenser 24 during the establishment of its discharge circuit will be equal to the difference between the voltage to which the condenser 24 is charged just prior to the instant the discharge circuit is established and the voltage-drop across the resistor 32 while the discharge circuit is broken.

centage.

age E1 therein, which is equivalent to the volt-' age-drop across resistor 32', will result in a cor'-' responding variation of the quantity Q of electricity discharged from the condenser 24' each time the discharge circuit is established. Thus,

since the voltage-drop across the resistor 32, that is E1, is low at low speeds and high and high speeds, it will be seen that the quantity Q7 of electricity discharged from condenser 24 each time'the discharge circuit is established at a low speed will be greater than that discharged fromthe condenser 24" each time the discharge circuit is:established at a: high speed.

The current in the discharge circuit and consequently the voltage-drop across the resistor 32 is thus not directly proportional to the rotational speed of the vehicle wheel with which the commutator device 23 is associated when the source,

corresponding to the storage battery 25, is of constant voltage. It will be apparent from Equation 3, however, that if the voltage of the source, which the battery 25 represents, is made relatively high in comparison to the voltage-drop across the resistor 32 at maximumvehicle speed,

then the, variation in the quantity of electricity discharged from the condenser 24 each time the discharge circuit is established at high and low speeds respectively will be a relatively low per- In such case, the current in the discharge circuit, and consequently the voltage-drop across the resistor 32, will approach closely to direct proportionality with the rotational speed of the commutator device.

The current in the discharge circuit may also be influenced somewhat by the time constant of the discharge circuit so that at the high speeds of vehicle travel it may be slightly less than would otherwise be the case. This eiTect can, however,

be minimized by providing a discharge circuit having a low time constant.

The. condenser unit 29 in the discharge circuit, being connected in parallel relation to the resistor 32 is charged to a voltage corresponding to the voltage-drop across the resistor 32- and stabilizes the fluctuations in the pulsating directcurrent in the discharge circuit under normal conditions of wheel deceleration.

' The condenser unit 29 functions also upon a reduction of the voltage across the resistor 32 occurring in response to deceleration of the wheels with which the commutator device 23 is associated to efiect a discharge of current locally in the discharge circuit through the resistor 32 and the winding of the polarized relay 3|. The current so discharged from condenser unit 29 will be equal to the product of the capacitance of the condenser unit and the change in voltage to which it is charged, that is, the change involtage across the resistor 32. Since the amount of the change in the voltage across the condenser unit 29 occurring in a given time interval will vary in proportion to the rate of deceleration of the vehicle wheel unit, the current discharged from condenser unit 29 locally in thedischarge circuit through the resistor 32 and the winding of relay 3| will correspond substantially to the rate of deceleration of the wheel unit.

' The winding of the polarized relay 3| is so connectedi in the branch circuit with the condenser unit 29 that the flow of current through the winding thereof in a direction to charge the condenser 29 to the voltage across the resistor 32 when such voltage is increasing and the vehicle wheel unit correspondingly accelerating will be such as to bias the contact member of the relay 3| to its open position. Conversely, when the voltage across the resistor 32 decreases, in response to deceleration of the vehicle wheel unit, the direction of flow of current discharged from the condenser unit 29 through the winding of the polarized. relay 3| is reversed and causes operation of the contact member of the relay to its closed position, if the current exceeds a certain value corresponding to a slipping rate of deceleration of the vehicle wheels. If the vehicle Wheelunit decelerates at a non-slipping rate, the condenser unit 29 likewise discharges current corresponding to the deceleration rate through the winding of the polarized relay 3| but the current is of insuiiicient value to cause operation of the contact member thereof to its closed position.

If the voltage-drop across the resistor 32 were directly proportional at all times to the speed of rotationof the Wheel unit, the'current discharged from the condenser unit 29 would always be the same for a given rate of deceleration of the Wheel unit regardless of whether the speed of rotation of the Wheel unit is high or low. However, as previously explained, the voltage-drop across the resistor 32 is not directly proportional to the rotational speed of the vehicle wheelunit and thus the rate of reduction of the voltage across the resistor 32 and the voltage across the terminals of the condenser unit 29 will be greater at the lower speeds than at the higher speeds for a given rate of deceleration of the wheel unit. It will be apparent that this is so because, at the higher speeds, a greater change in speed must occur in a given length of time, such as one sec- 0nd, in order to effect the same reduction in voltage-drop across the resistor 32 and therefore the same reduction in voltage on condenser 29 as at the lower speeds;

It follows, therefore, that the contact member of the polarized relay 3| may be picked-up, for example, at a rate of rotative deceleration of the vehicle wheel unit of seven miles per hour per second at the lower speeds and at a rate of fifteen miles per hour per second atthe higher speeds. However, since a rate of rotative deceleration of the vehicle wheel of seven miles per hour per second is never attained unless the vehicle wheel is slipping, the fact that the contact member of the polarized relay 3| will pick-up at different rates at the difierent speeds is nota practical diificulty because in no case will it pick-up unless the wheel is slipping. At the higher speed, the pick-up of the relay 3| is slightly delayed compared to low speeds;

If, as previously stated, the voltage of the source corresponding to the battery 25 is relatively high in comparison to the maximum voltage-drop across the resistor 32 so that the voltage-drop across the resistor 32 is almost directly proportional to the rotational speed of the vehicle wheel unit, then the per cent variation in the rate of rotative deceleration of the vehicle wheel unit effective" to cause pick-up of the contact member of the relay 3| at low speeds and at high speeds will be minimized. For example, the voltage of the source corresponding to the battery 25 may be such relative to the maximum voltage across the resistor 32 that the contact of the re lay 3| will be operated to closed position in response to a rotative deceleration of the vehicle wheel unit at a rate exceeding ten miles per hour per second, at low speeds and at a rate of rotative deceleration exceeding eleven miles per hour per second at high speeds.

Although the above-described apparatus is similar to the apparatus provided in the abovementloned copending application Serial No. 342,935 of John Canetta, it should be noted that the apparatus of the copending application is effective solely for detecting and registering the speed of rotation of a rotary element, such as a vehicle wheel, and is not effective to register the rate of change of speed, such as the rate of rotative deceleration, of a rotary element or vehicle wheel as is the apparatus which we have disclosed herein.

As is well understood by those skilled in the art, a polarized relay is of such nature that, once the contact member thereof is actuated to a given position in response to flow of current through the winding thereof in one direction, the contact member remains in such position until the direction of flow of current through the winding of the relay is reversed and exceeds a certain value. Thus when a wheel unit begins to slip, the contact member of the corresponding relay 3| is actuated to its closed position and remains in such position thereafter until the wheel unit begins to accelerate.

Each polarized relay 3| is arranged to control energization and deenergization of the magnet winding of the corresponding magnet valve device 2|.

The source of current for energizing the winding of each magnet valve 2| may be any suitable source of direct-current such as a storage battery 5|. The separate source 5| is provided for this purpose, rather than utilizing one of the sources 25, in order to avoid wide fluctuations in the terminal voltage E of the sources 25.

The magnet valves 2| are identical and of wellknown construction and, accordingly, a brief description thereof is deemed suflicient. Each magnet valve 2| comprises a suitable casing in which is contained a double-beat valve 54 which is urged normally to an upper seated position by a coil spring 55 and which is actuated to a lower seated position in response to energization of a magnet winding 56. In its upper seated position, the double-beat valve 54 is effective to establish communication through the branch pipe l8 of control pipe I5 to the associated brake cylinder l3. In its lower seated position, the double-beat valve 54 closes the supply communication through the branch pipe l8 and establishes a communication through which fluid under pressure is exhausted from the brake cylinder l3 through an exhaust port 51 at a rapid rate.

Operation of equipment shown in Fig. 1

is at atmospheric pressure and the brakes correspondingly released. Since the vehicle is traveling at a constant speed, the contact member of each of the relays 3| is in the open position thereof and consequently the magnet winding of the magnet valves 2| are deenergized so valve 2| is interrupted.

that communication between the control pipe l5 and brake cylinders I3 is open through the respective branch pipes l8.

If now the operator desires to effect an application of the brakes he may do so, after first shutting-off the propulsion power, by shifting the brake valve handle Ila into the application zone an amount corresponding to the desired degree of application of the brakes. The control pipe I5 is correspondingly charged to a pressure such as, for example, twenty-five pounds per square inch corresponding to the degree of displacement to the brake valve handle out of its brake release position and since the magnet windings of the magnet valve 2| are deenergized, fluid at a corresponding pressure is supplied through the branch pipes |8 to the corresponding brake cylinders |8 associated with the respective wheel units. The brakes associated with the wheel units are accordingly applied in accordance with the degree of pressure established in the brake cylinders. As long as the magnet windings of the magnet valves 2| remain deenergized the operator of the vehicle may vary the pressure in the brake cylinder |3 and correspondingly the degree of application of the brakes associated. with the wheels by varying or shifting the position of the brake valve handle.

If, during an application of the brakes or at the time that an application of the brakes is initiated, the wheels of a wheel unit begin to slip, further operation of the equipment occurs which will now be described. Let it be assumed that the left-hand wheel unit begins to slip. In such case, the contact member of the polarized relay 3| corresponding to such wheel unit is operated to its closed position to establish the circuit for energizing the magnet winding of the magnet valve 2| associated with the corresponding brake cylinder l3. The circuit for energizing the magnet winding of the magnet valve 2| is readily apparent from the drawings and needs no description.

Upon energization of its magnet winding the magnet valve 2| is operated to close communication through the. branch pipe |8 to the corresponding brake cylinder and cause fluid under pressure to be rapidly exhausted from the brake cylinder. Accordingly, substantially at the instant that the wheels 'of a wheel unit begin to slip, fluid under pressure is rapidly vented from the corresponding brake cylinder l3 to cause a corresponding reduction in the degree of application of the brakes associated with the slipping wheel unit. As a result of the rapid reduction in the degree of application of the brakes associated therewith, the slipping wheels promptly cease to decelerate and begin to accelerate back toward a speed corresponding to vehicle speed without decelerating to a locked or nonrotative condition and sliding.

As previously stated, the contact member of the polarized relay 3| remains in its closed position, once it is actuated thereto, until the current reverses in the operating winding of the relay. Thus, once the circuit for energizing the magnet winding of the magnet valve 2| is completed, it remains established until such time as the slipping wheels begin to accelerate at a rate exceeding a certain rate sufficient to restore the contact member of the relay 3| to its open position.

Upon the restoration of the contact member of the relay 3| to its open position, the circuit for energizing the magnet winding of the magnet The magnet valve 2| is thus restored to its normal position closing the exhaust communication and establishing the supply communication through the branch pipe I8 from the control pipe l-5 to the bralre cylinder l3.

The pressure in the control pipe 1&5 tends .to reduce due to the supply of fluid under pressure to the vented brake cylinder 13. However, due to the pressure maintaining feature of the brake valve l1, previously mentioned, fluid underpressure is automatically supplied to the control pipe l5 to maintain a pressure therein corresponding to the position of the brake valve handle, notwithstanding the resupply of fluidunder pressure to the brake cylinder l3. Thus, if the operator of the vehicle does not vary the position .of the brake valve handle Ila, :the fluid pressure restored in the brake cylinder 13 associated with the slipping wheel unit will be equivalent to :the pressure established in the control pipe [5.

If the pressure restored-inpthe brake cylinder 1 3 is effective .to cause thewheel unittoagain begin to slip, the above operation is repeated. Thus at no time are the wheels permitted to attain a locked or non-rtative condition and slide.

If the operator of the vehicle operates :the brake valve l! to reduce the degree of application of the brakes as the speed of the vehicle reduces, the fluid pressure reestablished in the brake cylinder associated with the slipping wheels will be correspondingly reduced and the likelihood of recurrence of wheel slipping lessened.

The contact member of the polarized relay 3| will ordinarily be restored to its open position, in response :to the acceleration of the slipping wheels, before the vehicle comes to a stop so thatthe magnet valve 2| will be correspondingly restored to its normal position. If it should happen, however, that the contact member of the relay '3! remains in its closed position, at the time the vehicle comes to a. stop, it will nevertheless be restored to its open position upon acceleration of the vehicle under propulsion power. Thus, the magnet valve 2| will always be properly conditioned .to provide open communication through the branch pipes l8 to the brake cylinders I3 at the time an application of the brakes is initiated.

When a vehicle comes to a complete stop in response to an application of the brakes, the

operator may vary the pressure in the brake cylinders I 3 as desired to secure any necessary degree of braking to hold the vehicle on a grade. Before starting the vehicle again, the operator may release the brakes simply by restoring the brake valve handle Ha to its brake release position in which position the fluid under pressure in the brake cylinders -l 3 is vented to atmosphere along with the fluid under pressure inthe control pipe I5 through the exhaust port [9 of the brake valve.

Equipment shown in Fig. 4

The equipment shown in Fig. 4 shows a modification of the arrangement shown in Fig. 1 and, being generally similar to the equipment shown in Fig. l, the corresponding parts in the two equipments are designated by the same reference numerals without further description. Only so much of the equipment shown in Fig. 4 that differs from that in Fig. 1 will accordingly be described.

The equipment shown in Fig. 4 differs from that in Fig. 1 with respect to the discharge circult associated with brush 28 of the commutator device 23. A transformer 30 is provided having a primary winding connected in the discharge circuit between the brush 28 and the ground connection 48 and having the terminals of the secondary winding ther of connected to the winding of a polarized relay 31a similar to the relay 3!. The contact member of the relay 3la is arranged to control the circuit for energizing the magnet winding of the magnet valve 2i (not shown), as indicated in Fig. 1.

A condenser 63 is connected in parallel relation with the primary winding of the transformer 30 for the purpose of smoothing out the fluctuating direct-current in the discharge circuit, which current varies substantially in proportion to the rotational speed of the wheels ll, as in Fig. 1,.

When the speed of rotation of the wheels H changes, the current energizing the primary Winding of transformer 30 changes at a corresponding rate. The magnetic flux coupling the primary and secondary windings of the transformer correspondingly reduces or increases at a corresponding rate and a voltage is thus induced in the secondary winding of the transformer which is proportional to the rate of change of current in the primary winding. Since the rate of change of current in the primary winding is proportional substantially to the rate of rotative deceleration or acceleration of the wheels, the voltage induced in the secondary winding of the transformer will likewise be substantially proportional to the rate of rotative deceleration or acceleration of the wheels. It will be apparent that the voltage induced in the secondary winding is of one polarity when the wheels decelerate and of the opposite polarity when the wheels accelerate.

The windings of the transformer 30 and the operating winding of the polarized relay 3|a are so designed and arranged that the voltage induced in the secondary winding of the transformer will cause energization of the winding of the relay 3la to a sufiicient degree to cause operation of the contact member thereof from its open to its closed position only in response to the rotative deceleration of the wheels I! at a rate exceeding a certain slipping rate. The operation of the contact member of the relay am in response to slipping of the wheels effects operation of the magnet valve 2| associated therewith to cause fluid under pressure to be released at a rapid rate from the associated brake cylinder.

It will be understood that the normal fluctuations .of the direct-current in the primary winding of the transformer when the wheels are rotating at a constant speed are effective to pro duce an alternating current of a corresponding frequency in the secondary winding of the transformer. The purpose of the condenser ESQ is to prevent the variation of the current in the primary winding at a sufficient rate normally that the voltage induced in the secondary winding will cause pick-up of the relay 35a. The capacitance of the condenser 60 is insufficient to interfere with the reduction of current in the primary winding at a sufficient rate to cause pickup :of the relay 3la in response to slipping of the wheels II. If the number of contact fingers 4| on the commutator device 23 is large so that the frequency of charge and discharge of the condenser 24 is high, then condenser 60 may be omitted because the pulsations of the direct-current in the discharge circuit will then be less likely to produce an undesired pick-up of the relay Ma. The condenser 60 may likewise be omitted if the relay 3la is made to be slow-acting. If relay 3Ia is slow-acting it will respond to a continued rapid reduction of the current in the discharge circuit occurring only when the wheels slip but not to the normal fluctuating changes in current in the discharge circuit during normal operation.

When the pressure of the fluid in the brake cylinder associated with the slipping wheels is reduced sufliciently, the wheels cease to decel-,

crate and begin to accelerate back to a speed corresponding to car speed. Acceleration of the wheels causes an increase of the current in the discharge circuit including the primary winding of the transformer 30 and consequently a voltage of reverse polarity is induced in the secondary winding. Such reversal of polarity of voltage induced in the secondary winding of the transformer causes the contact member of the relay 3la to be restored to its open position interrupting the circuit for energizing the magnet winding of the magnet valve 2|. The magnet valve is accordingly restored to its normal position closing the exhaust communication from the brake cylinder and reestablishing the supply communication thereto.

In view of the complete description of the equipment shown in Fig. 1, it is believed unnecessary to further describe the equipment shown in Fig. 4.

Equipment shown in Fig. 5

The equipment shown in Fig. 1 is satisfactory for a single rotary element or a limited number of rotary elements, such as the wheels of a single car, but does not lend itself in a practical manner to a brake control equipment for a train of cars. It will be apparent that the provision of a separate storage battery 25 for each wheel unit of train of cars would necessitate a large number of storage batteries, the initial cost, as well as service and maintenance cost, of which would present practical difliculties.

We have accordingly provided the brake control equipment shown in Fig. 5 to illustrate the application of our invention in a practical manher to a brake control equipment for a train of cars. The equipment shown in Fig. 5 differs from that shown in Fig. l in providing a single voltage source in the form of a generator I5 to act as the voltage source for all of the wheel units on a train of cars in place of a large number of separate batteries 25.

The generator is adapted to be driven at a constant speed in the manner presently to be described and provides a voltage which, as distinguished from the constant voltage of the batteries 25, varies with the speed of travel of the train. As will be explained more fully hereinafter, the generator 15 is a compound-wound generator of the direct-current type having an over-compounded voltage characteristic so that the terminal voltage of the generator varies in proportion to the total current supplied thereby to the separate commutator devices 23 associated with the respective wheel units, which current in turn varies in accordance with the speed of travel of the train.

The purpose of providing a generator with an over-compounded voltage characteristic is to secure a more uniform pick-up point for the relay 3| over a wide range of variation of train speed.

It will be recalled that in the equipment shown in Fig. 1, the relays 3| are not picked-up at exactly the same rate of rotative deceleration of a corresponding wheel unit because the quantity Q of electricity discharged from the condenser 24 when the discharge circuit is established is higher at low speeds than it is at high speeds, thereby causing variation in the voltage-drop across the resistor 32 which is not directly proportional to the rotational speed of the wheels. By so designing the generator 15 that the increase in the terminal voltage of the generator under load conditions over the no-load voltage thereof is substantially equal to the voltage-drop across the resistor 32 at any given speed, it will be seen that the amount of reduction in Voltage impressed on the condenser 24 each time the discharge circuit therefor is established will be a constant.

In other words if E represents the no-load voltage of the generator and e the increment of increase of terminal voltage of the generator under load conditions for a given voltage-drop 6 across resistor 32, the amount of change D in voltage on the condenser 24 each time the discharge circuit therefor is established may be expressed mathematically as follows:

That is, the amount of change of the voltage impressed on condenser 24 each time the discharge circuit therefor is established is a constant.

By reference to Equation 3, it will thus be seen that the quantity Q of electricity discharged from the condenser each time the discharge circuit therefor is established will be substantially constant and, therefore, as previously explained, the current in the discharge circuit will be theoretically directly proportional at all times to the rotational speed of the wheel unit.

In the case of a single rotary element, having a voltage source in the form of an over-compounded generator, the amount of the reduction in the voltage-drop across the resistor 32 and that across the condenser unit 29 effected in a given interval of time when the wheel unit is decelerating will thus be substantially constant for a given rate of deceleration. Accordingly, the current discharged from the condenser unit 2.9 locally in the discharge circuit through the winding of the relay 3i, upon deceleration of the wheel unit will be substantially the same for a given rate of deceleration regardless of whether the speed of rotation of the wheel unit is high or low. In such case, therefore, the relay 3| in the discharge circuit will be picked-up at substantially the same rate of rotative deceleration of the wheel unit whether the speed of rotation of the wheel unit is high or low.

In the equipment shown in Fig. 5, wherein the condensers 24 associated with a large number of wheel units are charged by the generator 15, the terminal voltage of the generator will vary in accordance with the charging current which is in turn proportional to the speed of the train. Thus, if an individual wheel unit begins to slip, the voltage to which the condenser 24 in the charging circuit of the corresponding wheel unit is charged is not reduced in accordance with the speed of the slipping wheel. The reduction in the voltage impressed on the condenser 24 associated with a slipping wheel when the dis charge circuit therefor is established accordingly increases somewhat with the reduction in speed of the slipping wheel because of the greater reduction in the voltage-drop across resistor 32 in comparison to the drop in voltage of the generator. The quantity of electricity discharged from such condenser .24, each time the discharge circuit therefor is established, accordingly does not remain exactly constant but increases slightly. However, since the voltage supplied by the generator I5 is adjusted initially in accordance with the speed of the vehicle, the variation from a constant value of the quantity of electricity discharged from the condenser each time the discharge circuit is established will be less than in the case of a constant voltage source.

It follows, therefore, that while the voltagedrop across the resistor 32 associated with a slipping wheel is .not exactly proportional to the speed of rotation of the slipping wheel, it will be more nearly so than in the case of a constant voltage source. Accordingly, the current discharged from the condenser unit 29 locally through the winding of the relay 3| upon the slipping of an individual wheel unit will be more nearly uniform for a given rate of deceleration than in the case of a constant voltage source.

As previously indicated with respect to the embodiment shown in Fig. 1 the current in the discharge circuit of each condenser 24 of the embodiment shown in Fig. 5 may tend to be somewhat reduced at high vehicle speeds due to the influence of the time constant of the discharge circuit. This effect can be approximately compensated for by the proper over-compounding of generator I5.

Considering the equipment shown in Fig. 5 in detail, it will be seen that the equipment shown is for a single railway car having two four-wheel trucks located respectively at opposite ends of the car, only one wheel of each shown.

The pneumatic apparatus whereby the operator controls the supply and release of fluid under pressure to and from the brake cylinders |3 differs somewhat from that shown in Fig. 1 and will be briefly described. As in Fig. 1, the main reservoir I6 is provided but the reservoir is located at the center of the car and is constantly connected to a train pipe, hereinafter called the supply pipe 6|. A brake valve ll of the selflapping type is provided for controlling the pressure in a control pipe l5 just as. in Fig. 1. The two pipes I5 and 6| extend from end to end of the car and are provided with suitable hose couplings 6.2 and angle cocks 63 in conventional manner whereby to connect the sections of these pipes on successive cars. Connections are established between the brake valve I1 and the pipes I5 and 6| respectively by branch pipes 64 and 65 in which are interposed manually operated valves 66. Valves 66 are turned to open position when it is desired to control the pressure in the control pipe l5 from the brake valve H on the corresponding car. When it is desired to control the pressure in the control pipe I5 by a brake valve located on another car, not shown, the valves 65 in both branch pipes 64 and 65 are closed thus rendering the brake valve I! on the shown car non-operative.

Instead of providing an individual communication between each brake cylinder and the control pipe I5 as in Fig. 1, the brake cylinders for each truck are controlled by a relay valve device 68, of well-known construction, which is in turn controlled according to the fluid pressure in control pipe l5 supplied thereto through a branch pipe |8 of pipe l5 under the control of a magnet valve 2|.

The relay valve 68 is of a super-sensitive high capacity type and is arranged to supply fluid unwheel unit being I der pressure .from the supply pipe 6|, to which it is connected by a branch pipe 69, to the brake cylinders I3 through a brake cylinder pipe 1| in response to the operating fluid pressure supplied to the pressure chamber thereof through the branch pipe l8 from the control pipe |5. When the pressure in the control pipe I5 is at atmospheric pressure the relay valve device 68 causes fluid under pressure to be exhausted to atmosphere through .an exhaust port thereof. When fluid under pressure is supplied from the control pipe I5 to the pressure chamber of the relay valve device .68, the relay valve device operates to cause fluid under pressure to be supplied from the supply pipe 6| to the brake cylinders I3 and establishes-a pressure therein corresponding to the pressure established in the control pipe l5.

A pressure operated switch 12, preferably of the snap-acting type, is connected by a branch pipe I3 to the control pipe I5 and is operatively controlled by the pressure therein. Any suitable type of pressureoperated switch may be provided. As diagrammatically shown, the pressure switch I2 comprises a contact member a which is adapted to be snapped out of engagement with a pair of associated stationary contact members when the pressure in the control pipe |5 is reduced below a certain low pressure, such as five pounds per square inch. When the pressure in the control pipe increases above such pressure, the contact member a of the pressure switch I2 is snapped into contact with its associated pair of contact members. The function of the pressure switch I2 will be explained hereinafter.

As in Fig. 1, each wheel unit of the equipment in 'Fig. 5 is provided with an axle-driven commutator device '23 for alternately establishing a charging circuit for a condenser 24 and a discharge circuit including a resistor 32, a condenser unit 29, and a polarized relay 3|. Instead of'providing a separate battery source, such as the storage battery 25, in each condenser charging circuit for each wheel unit, the equipment shown in Fig. 5 provides a single source of direct-current potential, in the form of the compound-wound generator I5 previously mentioned, the terminal voltage of which is impressed on a pair of train wires 11 and I8. The train wires 11 and I8 extend from end to end of the car and are provided with suitable couplers I9 whereby the sections of the train Wires on successive cars may be connected.

The brush 2! associated with the commutator device 23 of each wheel unit .is connected .by a wire 45 to the train Wire 1! which will hereinafter be referred to as the positive .train wire. The brush 26 associated with the commutator device 23 of each wheel unit is connected by a wire 46 to the train wire I8, the condenser 24 being interposed in the wire 46. The train wire I8 will hereinafter be .referredto as the negative train wire.

The discharge circuit including the parallelconnected resistor 32 and series-related condenser unit 29 and polarized relay 3| are connected in a circuit between the brush 28 associated with each commutator device 23 of each wheel unit and the negative train wire I8.

The contact members of the two polarized relays 3| for each wheel truck are arranged in parallel relation so that the operation of either relay, eifected in response to slipping of the corresponding wheel unit, may establish a circuit for energizing the magnet winding of the magnet valve 2| for the corresponding truck.

The source of current for energizing the magnet windings of the magnet valves 2| on each car is a storagebattery 8| which is indicated as being the usual car lighting battery. As indicated by the legend in Fig. 5, the storage battery BI is adapted to be maintained fully charged by a charging generator and apparatus in the usual manner.

The generator 15 is driven by a motor 82 of the shunt wound direct-current type. Motor 82 is operated by current supplied from the storage battery 8|, a knife switch 83 being provided for controlling the circuit connections between the motor 82 and the battery 8|.

In order to supply a substantially constant battery voltage to the motor 82, a voltage-regulator 84, of suitable type, is provided. The voltageregulator shown in Fig, is of the type shown and described on page 98 of the October 1923 issue of the Bell System Technical Journal and is accordingly notour invention.

Briefly, the voltage regulator 84 comprises a vacuum tube of the three electrode type having a plate 81, grid 88 and filament 89.

The filament 89 is heated by current supplied from a suitable source, such as a battery 9|, and the current through the filament is controlled by a suitable rheostat 92.

The grid 88 is connected by a wire 93 to an intermediate point of connection between two resistors 94 and 95 the outer ends of which are connected respectively to wires 98 and 91 connecting the motor 82 to the battery 8|.

The plate 81 is connected by a wire 98 to the wire 98. A third resistor 99 is interposed in the wire 96 between the respective points of connection thereto of the plate 81 and of the resistor 94.

In operation, an increase of the battery voltage raises the grid potential, thereby increasing the current through the tube and the resistor 99. Assuming the resistances of the resistors 95, 94 and 99 to be r1, m and 13 respectively, and the mutual conductance of the tube 86 to be y, it may be readily shown that by such choice of resistances and tube that The voltage impressed on the terminals of the motor 82 will be constant.

A voltage-regulator of the type described is adapted to maintain a substantially constant voltage supply over a wide range of variation of battery voltage. Thus, notwithstanding variations of the terminal voltage of the battery 8|, the voltage impressed across the terminals of the motor 82 will remain substantially constant and the motor will therefore operate at a substantially constant speed.

The motor 82 comprises a rotary armature winding 82a and a shunt field winding 82f. As is well known, the shunt motor has a relatively fiat or constant speed characteristic over a relatively wide range of load current.

The generator comprises an armature winding 15a. a shunt field winding 15), and a series field winding 15s. As shown, the shunt field winding l5f is connected directly across the brush terminals of the armature winding 15a so that the generator is what is commonly known as short shunt connected.

An electrical condenser I95 is connected between the output terminals of the generator 15, that is between one brush terminal of the armature winding 15a and the outer terminal of the series field winding 15s for the purpose of absorbing minor fluctuations in the output voltage of the generator due to the fluctuating current supplied to charge the condensers 24 associated with the different wheel units. Current is supplied from the output terminals of the generator 15 to the train wires 11 and 18 by branch wires I96 and I01 respectively. A double pole knife switch I98 is provided for the purpose of interrupting the connections between the output terminals of the generator 15 and the train wires 11 and 18 when desired.

In one of the branch wires, for example the wire I81, is interposed the pressure switch 12. Since the pressure switch 12 is operated to closed position only upon an application of the brakes, it will be seen that when the vehicle is traveling along the road with the brakes released, no current is supplied from the generator 15 to the charging circuit associated with each wheel unit. Accordingly the generator I5 is driven at noload when the vehicle is traveling along the road under power with the brakes released.

The relation and design of the field windings 15] and 15s of the generator 15 are such as to obtain an over-compounded voltage characteristic so that the terminal voltage of generator 15 impressed on train wires 11 and 18 increases and decreases as the speed of the car or train increases and decreases, respectively.

It will be apparent that the current supplied to charge the condensers 24 varies in direct proportion to the frequency of establishment of the charging circuits therefor, and thus according to speed of travel of'the car or train. Accordingly since the load current of generator 15 flowing through the series field winding 15s varies with the speed of travel of the car or train, the compounding of the generator may be so designed that the degree of increase in terminal voltage of the generator over the no-load voltage thereof will vary with the speed in unison with the variation in the voltage-drop across resistor 32 in each of the discharge circuits, as previously pointed out in connection with Equation 4.

For reasons previously explained in connection with the equipment shown in Fig. 1, the voltage supplied by the generator is preferably relatively high compared to the voltage drop across resistors 32. The no-load terminal voltage of generator 15 may, therefore, be of the order of five hundred volts and the maximum voltage-drop across the resistors 32 of the order of fifty volts.

When a plurality of cars are connected together in a train, only one motor-generator equipment need be connected to the train wires 11 and 18, the motor-generator equipments on other cars being cut-out of operation by means of the knife switches 83 and [08. It is desirable to have only one motor-generator equipment in operation at one time because of the difliculty of operating a plurality of generators in parallel relation. Obviously, in the case of modern high speed passenger trains in which the cars and power-unit remain coupled and do not travel as single cars, there is no need to provide a motor-generator set on more than one car. This one car may be and preferably is the power car.

It will be understood, therefore, that the greater the number of cars connected together, the greater is the current load of the generator 15 connected to the train wires l1 and 18. It is I with only one car in use, a maximum amount of the resistor Ill is connected in parallel relation to series field winding 158, thus diverting a minimum percentage of current from the series field winding. As the number of cars in the train increases, the contact arm H2 is positioned correspondingly to reduce the amount of the resistor III in parallel relation to the series field winding 75s so that the percentage of current diverted from the series field winding 15s increases correspondingly with the increase in the number of cars in the train. It will be seen that by suitably adjusting the position of the contact arm H2 in accordance with the number of cars in the train, at the time the train is made up, a substantially uniform overcompounded voltage characteristic of the generator 15 relative to the speeds of the train may be obtained, notwithstanding variation ln the number of cars in the train.

In view of the shown in Fig. 1, it is believed that the operation of the equipment shown in Fig. 5 will be readily understood from the above description of the parts of the equipment without any further specific description of the operation.

Summary Summarizing, it will be seen that we have disclosed several embodiments of vehicle brake control apparatus including a novel electrical device responsive to the rate of rotative deceleration of a Wheel or wheel unit of the vehicle for controlling the degree of the brake application and particularly adapted to be responsive to the deceleration of an individual wheel or wheel unit of the vehicle at a slipping rate for effecting a rapid release of the brakes associated with the slipping wheels to prevent the sliding thereof.

The electrical device responsive to the rate of rotative deceleration of a vehicle wheel comprises a commutator or rotary switch device operated in accordance with the rotational speed of the vehicle wheel for alternately charging a condenser to the voltage of a voltage-source and discharging it into a discharge circuit at a frequency proportional to the rotational speed of the vehicle wheel. Another condenser of relatively large capacity with respect to the first condenser is connected in the discharge circuit in such a manner as to cause a local discharge of current therefrom through the winding of a relay substantially in accordance with the rate of deceleration of the vehicle wheel. The relay is adapted to be picked-up only in response to a current exceeding a certain value and corresponding to a certain rate of rotative deceleration of the vehicle wheel unit occurring only when the wheel unit slips for elfecting the rapid release of the brakes associated with the vehicle wheel.

In one embodiment, the primary winding of a transformer is connected in the discharge circuit associated with the commutator device while the secondary winding of the transformer is connected to the operating winding of the relay. In this case, the reduction of the current in the disdescription of the equipment charge circuit in accordance with the reduction in the speed of the vehicle unit at a slipping rate causes a sufiicient voltage to be induced in the secondary winding of the transformer to cause pick-up of the relay and a consequent rapid release of the brakes.

In another embodiment, a single voltage source, in the form of an over-compounded generator driven at a constant speed, is provided instead of a plurality of separate sources, such as storage batteries, for supplying current to charge the condensers associated with all the separate wheel units of a car or train. Thus instead of charging the condensers associated with the commutator devices to a constant voltage each time the charging circuit therefor is established, the voltage varies with the speed of travel of the car. This arrangement enables the pick-up operation of the relays for efiecting the rapid release .of the brakes on a slipping wheel more nearly at the same slipping rate of deceleration, over a wide range of car speed, than the other embodiments.

The last described embodiment is particularly adapted for operation in connection with a train of cars. Since the current load on the generator varies with the number of cars, a diverter or resistor is connected in shunt relation to the series field winding of the generator and adjusted to different positions according to the number of cars in the train so that notwithstanding the variation in the current load of the generator in accordance with the number of cars, a substantially uniform over-compounded voltage characteristic relative to train speed is obtained.

It will be understood that the electrical apparatus responsive to the rate of change of speed of a vehicle wheel or wheel unit may be employed in other situations than brake control equipment for registering the rate of change of speed of any rotary element. Accordingly, while we have shown and described several embodiments of our invention particularly as embodied in connection with vehicle brake control equipment, it will be apparent that various omissions, additions, and modifications may be made in the embodiments shown without departing from the spirit of our invention. It is accordingly not our intention to limit the scope of our invention except in accordance with the terms of the appended claims.

Having now described our invention, what we claim as new and desire to secure by Letters Patent is:

1. In a vehicle wheel brake control equipment of the type having means under the control of the operator for controlling the application and the release of the brakes associated with the wheels of the vehicle and control means operative to effect a rapid reduction in the degree of application of the brakes associated with a vehicle wheel, the combination of a source of direct-current voltage, an electrical condenser, means providing a discharge circuit for said condenser, means effective to cause said condenser to be alternately charged to the voltage of said source and discharged into said discharge circuit at a frequency proportional to the rotational speed of the said vehicle wheel to cause a directcurrent to flow in the discharge circuit substantially proportional to the rotational speed of the said vehicle, and means responsive only to the change of current in said discharge circuit at a rate exceeding a certain rate which occurs only when the said wheel slips for effecting operation of said control means.

' 2. In a vehicle wheel brake control equipment of the type having a brake cylinder effective to cause application of the brakes associated with a wheel of the vehicle in accordance with the fluid pressure established therein and operative upon the release of fluid under pressure therefrom to effect the release of the brakes, means under the control of the operator for causing fluid under pressure to be supplied to said brake cylinder and released therefrom to effect application and release of the brakes, and electro-responsive valve means effective normally to permit the supply of fluid under pressure to the brake cylinder and operative to prevent the supply of fluid under pressure thereto and effect an exhaust of fluid under pressure from the brake cylinder at a rapid rate, the combination of a source of direct-current voltage, an electrical condenser, means providing a discharge circuit for said condenser, means effective to cause said condenser to be alternately charged to the voltage of said source and discharged into said discharge circuit at a frequency proportional to the rotational speed of the said vehicle wheel to cause direct-current to flow in the discharge circuit substantially proportional to the rotational speed of said vehicle wheel, and means responsive only to the change of current in the discharge circuit at a rate exceeding a certain rate which occurs only when the said wheel slips for effecting operation of said electro-responsive valve means.

3. In a vehicle wheel brake control equipment of the type having means under the control of the operator for effecting application and release of the brakes associated with wheels of the vehicle, and control means operative to control the degree of application of the brakes, the combination of a source of direct-current voltage, an electrical condenser, a discharge circuit for said condenser including a resistor and a second electricai condenser in parallel with said resistor, means effective to cause the first said condenser to be alternately charged to the voltage of said source and discharged into said discharge circuit at a frequency proportional to the rotational speed of a vehicle wheel to cause a direct-current to flow in the discharge circuit and to cause said second condenser to be charged to a voltagecorresponding to the voltage-drop across said resistor and substantially proportional to the rotational speed of the vehicle wheel, said second condenser being effective to discharge current cally in the discharge circuit substantially proportional to the rate of reduction of the voltagedrop across said resistor, and means responsive to the current discharged from said second condenser in the discharge circuit for controlling said control means.

4. In a brake control equipment for a train of vehicles, the equipment being of the type having means under the control of the operator of the train for effecting application and release of the brakes associated with the wheels on all vehicles of the train and additional control means for each of a plurality of different groups of wheel units for respectively controlling the degree of application of the brakes associated with the wheel units of the corresponding group, the combination of a compound generator of the directcurrent type driven at a substantially-constant speed, said generator having a series fleld winding and a shunt field winding so designed and constructed that the generator has an over-com- 75 circuit at a rate exceeding a certain rate for efpounded voltage characteristic variable according to the variation of the current energizing the series field winding, an electrical condenser for each of a plurality of wheel units on each of the vehicles of the train, a discharge circuit including a resistor for each of said condensers respectively, individual means associated with each wheel unit respectively effective to cause the corresponding condenser to be alternately charged to the voltage delivered by said generator and discharged into the corresponding discharge circuit at a frequency proportional to the rotational speed of the corresponding wheel unit to cause a direct-current to flow in the corresponding discharge circuit, means associated with the series field winding of said generator for so controlling the amount of current therethrough in proportion to the number of vehicles in the train as to cause the generator to produce a substantially uniform over-compounded voltage characteristic relative to train speed whatever the number of vehicles in the train, the voltage characteristic of the generator being such that the voltage delivered by the generator under load exceeds the no load voltage thereof by an amount corresponding to the voltage-drop across the resistor in the discharge circuit of each wheel unit, each condenser being effective correspondingly to discharge substantially the same quantity of electricity each time the discharge circuit therefor is established so that the direct-current flowing in the discharge circuit for each condenser is substantially proportional to the rotational speed of the corresponding wheel unit notwithstanding a wide variation in the speed of the wheel unit, and individual means for each discharge circuit responsive to the rate of change of current therein for controlling a corresponding one of said additional control means.

5. In a vehicle brake control equipment of the type having means under the control of the operator of the vehicle for effecting application and release of the brakes associated with the vehicle wheels and additional control means operative independently of the operator for effecting a reduction in the degree of application of the brakes associated with an individual wheel unit of the vehicle, the combination of a source of directcurrent voltage, an electrical condenser, a circuit, a switch device having a rotary element rotatable according to the rotational speed of a vehicle wheel and three brushes stationary with respect to said rotary element, said rotary element including a continuous ring of conducting material having a plurality of laterally projecting contact fingers of conducting material spaced substantially equal distances apart circumferentially of said ring, one of said brushes continuously engaging said ring and the remaining two of said brushes being so positioned with respect to each other as to alternately engage the contact fingers, the said one brush and one of the remaining two brushes being effective to control the connection between said condenser and said voltage source and said one brush and the other of said two brushes being effective to control the connection of said condenser in said circuit whereby said condenser is alternately charged to the voltage of said source and discharged into said circuit at a frequency proportional to the rotational speed of a vehicle Wheel to produce a direct-current in said circuit substantially proportional in degree to the rotational speed of the wheel, and means responsive only to a change of current in said fecting operation of said additional control means.

6. In a vehicle wheel brake control equipment of the type having means under the control of the operator for effecting application and release of the brakes associated with the wheels of the vehicle and additional control means for each of a plurality of wheel units operative independently of the operator of the vehicle for effecting a reduction in the degree of application of the brakes associated with the corresponding wheel unit, the combination of a compound generator of the direct-current type driven at a substantially contant speed, said generator having a series field winding and a shunt field winding so designed and constructed that the generator has an overcompounded voltage characteristic variable according to the variation of the current energizing the series field winding, an electrical condenser for each of a plurality of wheel units of the vehicle, a discharge circuit including a resistor for each of said condensers respectively, individual means associated with each wheel unit respectively effective to cause corresponding condensers to be alternately charged to the voltage delivered by said generator and discharged into the corresponding discharge circuit at a frequency proportional to the rotational speed of the corresponding wheel unit whereby to produce a directcurrent in the corresponding discharge circuit varying with the rotational speed of the wheel unit to cause the voltage drop across the resistor in said discharge circuit to vary upon variation in the speed of the vehicle, said generator having such a voltage characteristic that the voltage delivered by the generator under load exceeds the no-load voltage delivered by an amount corresponding to the voltage-drop across the resistor in the discharge circuit of each wheel unit, each condenser being efiective correspondingly to discharge substantially the same quantity of electricity each time the discharge circuit therefor is established thereby to cause the direct-current flowing in the discharge circuit of each condenser to be substantially proportional to the rotational speed of the corresponding wheel unit notwithstanding a wide variation in speed of the vehicle, and individual means for each discharge circuit operatively responsive to a change of the current therein at a rate exceeding a certain rate for effecting operation of the corresponding additional control means.

7. In a vehicle wheel brake control equipment of the type in which application and release of the brakes associated with the wheels of the vehicle is effected under the control of the operator, the combination of a source of direct-current voltage, a first condenser, a resistor, a second condenser, a relay having a winding, said second condenser and the winding of said relay being connected serially to each other and in shunt relation to said resistor, means operative to cause said first condenser to be alternately charged to the voltage of said source and discharged through a discharge circuit including said resistor said second condenser and the winding of said relay at a frequency proportional to the rotational speed of a wheel oi. the vehicle whereby to cause a direct-current voltage-drop to be established on said resistor effective to charge said second condenser, said second condenser being effective to discharge current locally through the winding of said relay and said resistor to cause operative response of said relay when the voltage across said resistor reduces at a rateexceeding a certain rate, and means controlled by said relay and effective in response to operation of said relay for causing a reduction in the degree of application of the brakes associated with said vehicle wheel.

8. In a vehicle wheel brake control equipment of the type in which application and release of the brakes associated with the wheels of the vehicle is eilected under the control of the operator, the combination of a source of direct-current voltage, a first condenser, a resistor, a second condenser, a polarized relay having a winding and a contact operative from a normal position to a different position in response to a current exceeding a certain value and flowing in one direction through said winding and remaining in said different position until a current exceeding a certain value and flowing in the opposite direction through said winding occurs whereupon it is restored to its normal position, said second condenser and the winding of said relay being connected serially to each other and in shunt relation to said resistor, means operative to cause said first condenser to be alternately charged to the voltage of said source and discharged through a discharge circuit including said resistor said second condenser and the winding of said relay at a frequency proportional to the rotational speed of a wheel of the vehicle whereby to cause a direct-current voltage to be built-up across said resistor effective to charge said second condenser, the current supplied to charge said second condenser fiowing in the said opposite direction through the winding of said relay and being substantially proportional to the rate of increase of voltage across said resistor, said second condenser being effective to discharge current in the said one direction through the winding of said relay and said resistor substantially proportional to the rate of reduction of the voltage-drop across said resistor, and means operative in response to operation of the contact of said relay to its different position to eifect a rapid reduction in the degree of application of the brakes associated with said wheel and in response to restoration of the contact of said relay to its normal position to terminate the reduction in the degree of application of the brakes.

9. In a vehicle wheel brake control equipment of the type in which application and release of the brakes associated with the wheels of the vehicle is effected under the control of the operator, the combination of a source of directcurrent voltage, a first condenser, a resistor, a second condenser, a relay having a winding, said second condenser and the winding of said relay being connected in serial relation to each other and in shunt relation to said resistor, means operative to cause said first condenser to be alternately charged to the voltage of said source and discharged into a discharge circuit including said resistor said second condenser and the winding of said relay at a frequency proportional to the. rotational speed of a wheel of the vehicle whereby to cause a direct-current voltage to be established across said resistor elfective to charge said second condenser, said second condenser being efi'ective to discharge current through the Winding of said relay and said resistor in response to a reduction of the voltage across said resistor which current is substantially proportional to the rate of reduction of the voltage across said re-' sistor, said relay being operatively responsive to energizatlon of its winding by current discharged from said second condenser exceeding a certain" value and occurring only when the said vehicle wheel rotatively decelerates at a slipping rate, and means controlled by said relay and effective in response to the operation thereof for effecting a rapid reduction in the degree of application of the brakes associated with said wheel.

10. In a vehicle brake system having a control device operative, while the brakes are applied, to rapidly reduce the degree of application of the brakes on at least one wheel of the vehicle, in combination, a relay for controlling said control device, a first condenser effective to cause operation of said relay, a second condenser, and means associated with a wheel of the vehicle for causing alternate charging and discharging of said second condenser, discharging of said second condenser being effective to cause charging of said first condenser, and means relating said relay and said first condenser in a manner such that when said wheel slips said first condenser operates said relay.

11. In a vehicle brake system having a control device operative, while the brakes are applied, to rapidly reduce the degree of application of the brakes associated with at least one wheel of the vehicle, in combination, a first condenser, a charging circuit for said first condenser, a discharge circuit for said first condenser including a second condenser, means governed by the rotation of a wheel of the vehicle for alternately establishing one while interrupting the other of said charging and discharging circuits, to cause said second condenser to be charged as a result of the alternate charge and discharge of said first condenser, said means causing said second condenser to discharge at least a predetermined current upon slipping of said vehicle wheel, and electroresponsive means operative in response to said predetermined discharge current of the second condenser for effecting operation of the said control device.

12. In a vehicle brake system having a control device operative, while the brakes are applied, to rapidly reduce the degree of application of the brakes associated with at least one wheel of the vehicle, in combination, a first condenser, a charging circuit for said first condenser, a discharging circuit for said first condenser including a resistance element and a second condenser, means governed by the rotation of a wheel of the vehicle for alternately establishing one while interrupting the other of said charging and discharging circuits, to cause said second condenser to be charged as a result of the alternate charge and discharge of said first condenser, said means causing said second condenser to discharge at least a predetermined current through said resistance element upon slipping of said vehicle wheel, and electroresponsive means operative in response to said predetermined discharge current of the second condenser for effecting operation of the said control device.

JOHN CANETTA. PAUL N. BOSSART. 

